Vibrating system



March 14, 1961 J. RCiZ lKA 2,974,798

VIBRATING SYSTEM Filed Oct. 28, 1955 2 Sheets-Sheet 1 INL/ENTOR. .Tara:la zr ZJzzz /(a March 14, 1961 Filed Oct. 28, 1955 J. RlililKA VIBRATINGSYSTEM 2 Sheets-Sheet 2 INVENTOR. JAROSLAV RGEIEKA AGENT.

United States Patentf Q VIBRATING SYSTEM Jaroslav Rfiiika, 7'4Krizikova, Prague-Kaitlin, Czechoslovakia Filed Oct. 28, 1955, Ser. No.543,550

4 Claims. (Cl. 209-365) This invention relates to balanced vibratingsystems 2,974,798- Patented Mar. 14,

, :therefore necessary to choose the proper stiffness of the consistingof at least three aligned masses. Such systems may be used for instanceas reciprocating screens for grading such materials as sand, coal,broken stones, or

different minerals, as vibrating conveyors or the like.

Vibrating systems of this kind generally use counterweights which aresupposed to balance the movements of operating conditions, so that thereactions transmitted to the frame or foundation are generallyconsiderable. But

even if the masses are perfectly balanced, a forced drive of differentmasses transmitsto the driving shaft rather considerable forces whichmay be in equilibrium with respect to the whole system, but whichrequire the use of a drive means of large dimensions.

It is an object of the present invention to provide-a vibrating system,which may be perfectly balanced for different operating conditions andwhich reduces all reactions of the oscillating masses to a minimum, sothat the driving means can be reduced to a size capable of overcomingthe passive resistances and where the reaction to the driving forces areminimized.

A further object of the invention is to provide for a smooth starting ofthe system and the increase of speed up to operating conditions withoutundue vibrations.

Further advantages and objects of this invention will be apparent fromthe following description with reference to the accompanying drawings,where Fig. I is a schematic layout of a reciprocating screen consistingof three separate screen frames, Fig. 2 is a similar view of a screenwith five screen frames, and Figs. 3 and 4 are respectively an elevationand top view of a screen as shown in Fig. 1.

1 1o Claims priority, application Czechoslovakia Nov. 9, 1954 elasticelements 9 in order that the adjacent masses receive the proper phaserelation.

If-the screen 7 has the mass m-; and if its amplitude of vibration is x,the amplitude of vibration of screen 1 isy vand the stiffness of theelastic element 9 is c, the follow- .ing differential equation must befulfilled for the elastic element having one end leaning against themass m, and its other end brought to oscillations y=y cos wt: 9 Y

m i6+c(x-y cos wt) =0 1A partial solution of this equation will be i Ix=x cos wt where (JO-M7002 If the magnitude of the amplitudes should beequal, but

.'of. opposite sign, there must be It follows therefore, that thestillness of each of the elastic'elements 9 does not depend upon themagnitude *of the amplitudes of vibration, so that the system --is ofthe respective screens 1, 7 and 8. For an equilibrium The screenaccording to Figs. 1, 3 and 4 consists of the central substantiallyhorizontal screen frame 1 and two outer aligned screen frames 7 and 8.All frames are supported by substantially parallel bars 6, which are inturn supported by the solid frame or foundation 4. The

screen 1 is agitated by a set of two parallel bars 2 pivotal- I lyconnected at one end to cranks 13 of the shaft 3, which is supportedeither rigidly or elastically upon the frame 4 and which is driven forinstance by an electric motor 5 (Figs. 3 and 4). The screens 7 and 8 areconnected to the screen 1 only by means of elastic elements 9, arrangedin the prolonged side bars 11 of the frame 1 and acting on the screens 7and 8 in directions perpendicular to the support members or parallelbars 6 for such screens, as is apparent in the drawings.

The axis of each of the elastic elements 9 lies practically in a planeincluding the center of gravity of the mass :driven thereby. As isapparent in Figs. 3 and 4, each side bar 11 has an opening 20 thereinand theelastic -elements 9 bear against the opposite end edges of the.opening 20yand against a lug 21 which projects laterally where r r-,,and r are the amplitudes of the oscillations of the respective massesand w the angular velocity of the oscillations.

If we substitute these terms in Equation 1 we receive m r w m r w -m r w=O 2 7 At the same time the sum of the moments of the osfcillatingmasses must be zero, if a balanced state is to be achieved. If wesuppose that the force P acts at a dis- .tance a from the force P andthe force P at a distance b from the force P the following conditionwill have to be fulfilled for an equilibrium of moments with respecttothe v..;7,; 8 half the' rnass of the central screen ,1,-: and t heircenters of gravity are equally spaced from the center of gravity of thecentral screen, the system will be balanced, if the amplitudes r and rare equal and in the direction opposite to that of the amplitude 11;. 77 A It is however possible to attain a balanced state even for differentmasses m and m and for differentamplitudes, and even for differentdistances aand b. We have thus the possibility ;to give for instance tothescreen 7 a larger amplitude of vibration than to the screen -1 and atthe same time to the screen 8 asmaller amplitude of vibration than tothe screen 1, as is often advantageous when gradingcertain material, andachieve simultaneous 1y, that the whole'system is balanced astoitsforces and the moments resulting from these forces. Similarly it ispossible to choose Within the limits of both fundamental equations themasses of the screens and the distances of their centers of gravity sothat the whole system may be easily adjusted to the required conditions.If the stifiness of the elastic elements 9 is chosen so that theadjacent masses always move in opposite directions, with amplitudes ofthe required magnitude, then the parallel bars 2 are transmitting to theframe only reactions which correspond to the passive resistances of thewhole system.

It should be mentioned that the system is working above the criticalfrequency with respect to the masses 7 and 8 and it is thereforenormally necessary to damp the oscillations which are originated whenincreasing'the fre quency from zero to the normal working frequency, andthis may be accomplished by suitable dampers, as indicated by referencenumber 10 on Fig. 3. As shown in Fig. 3 by way of example, each damper10 arranged between the elastic elements 9 and a driven mass representedby the screen frame 7 or 8 may be a conventional device comprising acylinder 22 secured to the related side bar 11 and containing a fluid,and a piston 23 reciprocable in the cylinder 22 and joined by a rod 24to the lug 21 projecting from the adjacent screen frame 7 or 8 so thatthe fluid in cylinder 22 acts on the piston 23 to damp the movements ofthe screen frame 7 or 8 relative to the screen 1.

The fact that the system works above the critical frequency of themasses 7 and 8 has the advantage that minor changes in masses or otherparameters do not-produce undue forces or oscillations under operatingconditions.

The system according to the invention may be however brought to fullworking frequency without dampers and without starting any undueoscillations by bringing thedriving shaft 3 to full speed at zero orrather small eccentricity of the crank 13 with respect to the shaft 3and by increasing thereafter the eccentricity until the required'am-.plitudes are attained. The change in eccentricity during operation maybe accomplished by any known means, for instance by changing therelative position of two eccentric discs. In a similar way the startingand stoppingof the whole system may be accomplished if a drive otherthan a crankdrive is used.

The oscillating system according to the invention is not limited tothree aligned individually oscillating masses,

and it is theoretically possible to use a larger number of such masses,so long as the conditions given by the Equations 1 and 3 are fulfilledfor such larger number of masses.

*Fig. 2 shows schematically a system with five aligned oscillatingmasses 1, 7, 8, 17, 18. The elastic elements 9 are here connected to theprolonged side bars 14, 15 of the screen frames 7 and 8. The mass 1 isagain directly driven. Otherwise all conditions described with referenceto the system according to Fig. 1 also apply to the system of Fig. 2,with the same possibility of choosing the magnitude of the masses,amplitudes and distances of the "centers of gravity. It is not necessarythat the'direct drive be of the mass 1, as the mass 7 or 8 mayalternatively receive the direct drive.

Sand -4 show-in elevation --a.nd top viewan em bodiment of the inventionemploying a horizontal reciprocating screen. The reference numbers usedin Fig. 1 are applied to the corresponding parts of Figs. 3 and 4. Inaddition there are shown the dampers 10 for damping oscillations whenstarting and stopping the drive. These dampers may have a linear ornon-linear characteristic and may be arranged as shown between theelastic elements and driven mass, or, alternatively, between the drivenmass and the frame or foundation of the system.

The system accordingto the invention maybe used for differentinstallations, as for vibrating screens, vibrating conveyors and thelike. The individual elements may be adjusted according to localrequirements. It is for instance possible to have the bars 6 rigidlyfixed to the frame or foundation 4 by means of torsional links or tohave the screen frames suspended from an overhead frame, or to use otherarrangements suitable for a given purpose.

By practically eliminating all so called dead oscillating masses, thatis, masses which do not perform anyuseful work, for example, masseswhich do not carry material, such as, masses acting solely as acounterbalance or oscillating supporting frames, a considerablereduction of the weight of the whole system is achieved, with acorresponding reduction of the driving and maintenance costs. Inaddition to reducing the weight of the oscillating masses, aconsiderable reduction of the stress upon the driving mechanism isattained, and the latter need only be sufliciently powerful to overcomethe passive resistances of the whole system. As a perfect balance offorces and moments may be achieved, practically no reactions need to betransmitted to the foundation so that undesirable vibration of thebuildings or other adjacent machines is avoided.

The system may be used either in the horizontal, vertical, or inclinedpositions of the aligned elements. No special precautions are requiredin case of minor frequency changes in the electricity in the supplylines and of minor irregularities in the feeding or grading of thematerial, which do not involve any substantial undesirable reactions, asthe system works above the resonant frequency of the masses 7 and 8, sothat the state of balance need not be so rigidly maintained. 7

What I claim is:

1. A vibrating system comprising at least three aligned masses, a fixedbase, substantially parallel elongated support members pivotallyconnected at their opposite ends to said base and each of said masses tosupport the latter for oscillation independently of each other aboutneutral positions wherein the related support members inclinesubstantially from the vertical, drive means carried by said base anddirectly connected to only one of said masses to forcibly oscillate saidone mass with an amplitude that is positively determined by said drivemeans, said support members and drive means constituting the soleconnections between said masses and said fixed base, elastic elementstransmitting oscillations from said one mass to the others of saidmasses and having stiifnesses causing the oscillation of adjacent massesin opposed phase relation so that the adjacent masses move in oppositedirections, said elastic elements exerting forces, when deformed, whichact along lines passing through the centers of gravity of the relatedmasses oscillated thereby and extending substantially perpendicular tothe support members for said related masses, the sum of the products ofthe values of said masses and of the amplitudes of oscillation thereofbeing zero and the sum of the moments of the oscillating masses withrespect to any point also being zero so that the system is fullybalanced at all amplitudes of oscillation. v

2. A vibrating system as in claim 1; wherein each of said elasticelements is in the form of a helical spring, and the line along whichthe latter exerts said force is in the direction of the axis of thehelical spring.

3. A vibrating system as in claim 1; wherein said drive tions impartedthereby to said one mass so that, in operating above the resonantfrequency of the system, said drive means can be adjusted to impart zeroamplitudes of oscillation during starting, and the amplitudes ofoscillation are increased only when said drive means approaches itsnormal operating speed, while the amplitudes of oscillation can bedecreased to zero before stopping said drive means, thereby to preventundesirable vibrations in passing through said resonant frequency.

4. A vibrating system as in claim 1, further comprising vibrationdampers connected to said other masses for damping the oscillationstransmitted to the latter.

References Cited in the file of this patent UNITED STATES PATENTS NortonJuly 20; 1915 Schieferstein et a1 Apr. 9, 1935 Linke et a1. Sept. 29,1942 FOREIGN PATENTS Great Britain of 1900 France Mar. 24, 1954 FranceDec. 8, 1954

